Implementation notes: See notification system improvements.

Acceptance Criteria:

• Organizers should have the option to receive notifications for:
  • They are added as an organizer of the event
  • Someone registered for the event
  • Someone unregistered for the event]
  • if participant changes registration status (public to private, or private to public)
  • Someone was added as a co-organizer
  • [maybe] An email was sent to the participants - but maybe not necessary if we have the "send me a copy of the email" feature
• The organizer can opt in or out of via Preferences
• Notifications should be off by default (except if added as organizer to event)